Cool concept with an intriguing story. Well done on completing something so complex for your first jam. After all, a journey of a thousand miles begins with a single step.
Collisions were a bit odd, too large maybe - a good rule of thumb is to make the ones the player needs to avoid smaller than they look (so the flower/tree/enemy) and the ones they want to hit larger than they appear (powerups). Not sure if there was something else I was doing wrong but I could only get the power up the 0 key (black hole circle attack) to work. It looked nice and was pretty powerful so well done. I was able to spam it to kill the enemies very quickly so maybe it should have a cooldown before it can be used again.